texts:
Why do we divide time into weeks?  Is there any celestial reason why humans do this?

one year: earth revolution around the sun
one month: moon revolution around the earth
one week: 7 days = ???
one day: earth rotation about its axis


texts: How many galaxies can be seen in a given patch of sky

texts:
Similar to the question asked here, but my question is not about what can be seen with the naked eye but rather what might be seen if pointing my Newtonian reflector (full specs outlined below) at an average point in the sky. (This is why my questions is different from the potential duplicate...)

I was doing this last night because it was cloudless and ok seeing, and whenever I point the scope at a given patch of sky I always see a much larger amount of objects (obviously) but how many of these additional dots are galaxies and how many are just nearby red dwarfs or average but more distant stars in the milky way?

Do galaxies ever appear as points of light similar to faint stars, or are they always more diffuse like Andromeda is through binoculars or my telescope? To be clear here, I'm not talking about the galaxies in our local group that are close enough to be discernable as actually fuzzy objects, but rather more distant galaxies that might be very bright (i.e. large elliptical galaxies). I feel as though I'm answering my own question here and that galaxies are only seen as diffuse objects and not points of light, but I can't think of a good way to test this hypothesis with my equipment.

Assume ideal conditions (low light pollution, perfect seeing, etc.) although I am also curious to know how much this changes if the light pollution conditions worsen, particularly in my backyard. For reference, I can somewhat make out the milky way on a cloudless, moonless night. Andromeda is not visible without small binoculars on any night here (or it is and my eyes just aren't trained enough to find it without them).

A better way to phrase my question might be this. Imagine if I were to remove all the stars in the milky way so that the only objects in the night sky were other galaxies. How densely populated with the sky be to the naked eye, and how densely populated would it be through my telescope?

Thanks for taking to the time to read my question(s)! I hope to be able to give my own answers one day.
Clear skies everyone.

Telescope specs:
NexStar 130mm
Aperature: 130mm
Focal Length: 650mm
Eyepiece: 9mm, 1.25" Plossl


texts: Statistics of the purposes of archeoastronomical sites?

texts:
Archeoastronomy is not the most prominent tag used here at astronomy SE. It can be defined as

the interdisciplinary or multidisciplinary study of how people in the past "have understood the phenomena in the sky, how they used these phenomena and what role the sky played in their cultures"

Beside this article, I also found a nice list of archaeoastronomical sites. What I have not found though is a statistics on the observational purposes of the various sites. Which kind of astronomical observations have most likely been made by these early observatories? It would be also interesting to know, at which earliest point of time which observation was possible. I am looking for a concise statistics of astronomical observations possible with ancient observatories, if that exists.
As a starting point might be the following list of reproducible observations possible with Stonehenge as extracted from a introductory astronomy article on Stonehenge

Northernmost moonrise
Southernmost moonrise
Northernmost moonset
Northern moonset minimum
Midwinter sunset
Midsummer sunrise

Further reading

Clive Ruggles and Michel Cotte (editors): Heritage Sites of Astronomy and Archaeoastronomy, 2012


texts: Are there any measurements of other galaxies indicating the existence of exoplanets?

texts:
Of course scientists assume there would also be exoplanets in other galaxies besides our own Milkyway.
Is it true that our telescopes are not good enough to see planets in other galaxies, nor by brightness changes of the stars nor by inclination changes of stars. If so could the total mass of those galaxies be an indication of the presence of exoplanets, or is dark matter a problem for that?


texts: Does the dust around SMBH's protect habitable planets from jets?

texts:
The supermassive black hole in the Milky Way is covered by dust as seen from here. Is it common that SMBH's are covered in dust in their galactic disks? Would that dust absorb and disperse a jet from an active galactic nucleus, so that the atmospheres of Earth like planets would be protected?

AGN jets build bubbles perpendicular to the galactic plane, but the jet could be oriented in any direction, right? The bubbles are shaped by general stellar winds from the disk, redirecting the jet streamed material towards the galactic poles, if I get that rigt.


texts: Why can't we see distant galaxies with the naked eye?

texts: If light keeps travelling in a straight line, why can't we see distant galaxies with the naked eye? Surely if you stared long enough, the light from them would eventually hit your eye? I apologize if this is a dumb question:)


texts: Is there any way a meteor can hit at less than escape velocity?

texts:
Note:  I have figured out one case:  The meteor is splash from an impact on a close-in moon.  I'm looking for any path from deep space.

My understanding is that anything from deep space will inherently pick up the escape velocity in it's fall and thus there is no possibility in the simple case.  I'm not so sure about what could happen after an encounter with one or more moons, though.


texts: If I could see from a Gravitational-Time dilated place to somewhere far which is not dilated, would I see fast moving people?

texts: Gravitational time dilation like the one shown in the movie Interstellar, causes time to move slowly for someone within the high gravity reference frame. Now let's say that from such a place, I was able to view through a telescope somewhere far away which is not gravitationally dilated. And assume that I am able to view the near live video stream of it. Would those people look fast moving?


texts: Could we detect an extraterrestrial signal with the SKA radio telescope?

texts:
As I have not seen this question answered and, following the rules: https://stackoverflow.blog/2011/07/01/its-ok-to-ask-and-answer-your-own-questions/ , I would like to answer this important question.

As you know, by 2027 we expect to have the biggest radio telescope already working: the Square Kilometre Array.

According to the former Interim Director General of the SKA project, Michiel van Haarlam, it will be possible to detect the radar of an extraterrestrial airport 60 light years away, once the initial stage of the project is completed.

However, a recent study also points out that the SKA could detect extraterrestrial airports 200 light years away.

Source: https://www.youtube.com/watch?v=ayqyb8XCtE0


texts: Can things move faster than light inside the event horizon of a black hole?

texts:
Black Holes are regions of space where things get weird [Citation Needed]. Past the event horizon of a black hole, any moving particle instantaneously experiences a gravitational acceleration towards the black hole that will cancel out it's current velocity, even light. That means that the gravity well of the black hole must be able to accelerate from -C¹ to 0 instantly². Given that fact, we can assume the gravitational acceleration of black holes is C/instant³. Given this, it stands to reason that in successive instants, the particle will be moving at speeds greater than C, because it is experiencing greater gravitational forces and continuous gravitational acceleration.

Does this actually make sense? Is there something I'm missing here? By this logic, it seems like anything inside of the event horizon of a black hole could and should move faster than C due to gravitational acceleration.

Edit: I showed this question to a friend and he questioned if the hypothetical particles that were radiating from the singularity (The photon traveling exactly away from the black hole) might be hawking radiation; that is, the gravitation acceleration of a black hole is only strong enough to curve the path of light around a non-zero radius (thus not actually stopping it, but altering it's course), and not powerful enough to decelerate light. Is this actually what hawking radiation is, or is he as confused as I am?

¹ Where movement towards the singularity would be considered a positive value, movement away from the singularity is a negative value, that is, anything moving at the speed of light away from the singularity would be moving with a velocity of -C relative to the singularity.

² If it couldn't accelerate from -C to 0 instantly, any photon traveling exactly away from the black hole would be able to escape the event horizon.

³ An instant is an arbitrary amount of time, it could be a fraction of a second, a second, a minute....


texts: Estimate the number of pixels required to map the full primary beam of a Radio Telescope station

texts:
I am practising some exam questions for a radio interferometry exam, and I am struggling with this question:

The physical size of a single LOFAR station, operating at 150MHz is about 50m.
Estimate the number of pixels which would be needed to map the full primary beam if one wished to include all LOFAR stations (maximum baseline ~ 800 km) at full resolution.

OK, so the resolution of the entire array is given by

Wavelength / Baseline Length which is 2m/800km = 2.5 x 10^-6 radians, or 0.52 arcseconds.

I don't know how to relate this angular resolution to the image size which I think is a 50m square.

Can anyone help with this?


texts: Would a direct hit by a small comet be catastrophic?

texts: Would a direct hit by a short-period comet with a 3 mile diameter nucleus cause enough damage on Earth to threaten or destroy human life and the ability to produce crops?


texts: Tables of aphelion/perihelion dates for other planets?

texts:
It's relatively easy to find tables for Earth aphelion and perihelion dates and times, such as this one:

http://www.astropixels.com/ephemeris/perap2001.html

But what about the other planets in the solar system? Are there tables or lists of aphelion and perihelion dates for them too? I checked Wikipedia, but it only lists perihelion distances and not dates, so it is insufficient.

Update:

This is the error I get on the SPICE web interface.


texts: what is the net effect of nodal and apsidal lunar precession?

texts: In apsidal lunar precession, the moon's elliptic major axis precesses eastward and completes one revolution eastward in 8.85 years.  Because the orbit is inclined relative to the ecliptic, basic geometry dictates that the ascending and descending nodes must also rotate about the ecliptic at the same rate (all else constant.)  But then there's nodal precession, rotating the nodes in the opposite (west) direction, one revolution every 18.6 years.  So what is the net effect of these two precessions on the positions of the nodes? Subtract the two?


texts:
Tonight, while looking at the night sky, I saw a moving object which I cannot assign to any cosmic or man-made object known to me.
The object looked like a star, and hadn't it been moving, it would have been indistinguishable from one. However, unlike usual objects in the night sky, its movement velocity was inconsistent, and its direction didn't follow a straight line, but kept digressing and then returning to the original path. It reminded me of a biker going through a crowd, or a car avoiding potholes. It moved quite quickly though, and traversed the sky in a couple of minutes.
What object is the description consistent with?


texts: How can we install a radar on radio telescopes like FAST or GMRT?

texts:
Recently I came across an article mentioning that ever since the failure of Arecibo telescope, we only have one asteroid radar imaging telescope which is Goldstone observatory.
The article also mentions the need of Asian (or any other country) radio observatory to upgrade their telescopes to telescope + radar system to take the place of Arecibo.
This made me wonder how can we upgrade such system instead of starting all over again (building a new telescope that could handle radar imaging as well).


texts: How do ground-based telescopes deal with earthquakes?

texts: Astronomical telescopes observe particular points in the sky for hours or even days, and they have to remain particularly steady for the duration of the observation, as far as I know. What happens when an earthquake shakes the ground? Does it ruin the observation? If so, how frequently does that happen?


texts: Regarding matter that has the highest redshifts, do we see such matter in every general direction we look (relative to Earth: up down left right front back)?


texts: Data reduction and photometry without IRAF?

texts:
The IRAF package is old.

I've been looking around for a more modern software to replace it in the processes of CCD data reduction and photometry, but haven't been able to find any.

The closest I've found is the PyRAF tool, but this seems more like a Python wrapper around IRAF rather than a replacement for it.

Is there some new software I might've miss or is IRAF really the only option even today?

Add:

I forgot to mention this, but I'm looking for tools that work under Linux and are free (open source + no charge), if possible. I will not pay (neither for a Windows license nor for a software package) to get rid of IRAF.


texts: When will the next transit of Earth be visible from Mars? Was the last one really on May 11, 1984?

texts:
@PM2Ring's comment mentions the story Transit of Earth written by the famous British science fiction writer, science writer and futurist,3 inventor, undersea explorer, television series host, Fellow of the Royal Astronomical Society and Commander of the Order of the British Empire and celebrated polymath Arthur C. Clarke in which the character's task is to record a transit of the Earth across the Sun's disk as seen from Mars.
According to the story, this happens on May 11, 1984.
The story also mentions that the previous occurrence would have been in 1905, and the following one would be 100 years following this one, presumably in 2084.

The radio has just printed a message from Earth, reminding me the transit starts in two hours, as if I’m likely to forget, when four men have already died so that I can be the first human being to see it, and the only one, for exactly a hundred years.
It isn’t often that Sun, Earth and Mars line up neatly like this. The last time was in 1905, when poor old Lowell was still writing his beautiful nonsense about the canals and the great dying civilization that built them.

Question: Were there in fact transits of the Earth as seen from Mars on these dates (in 1905, on 11-May-1984, and in 2084)? If they do occur at roughly 100 year intervals as suggested, there may in fact be people on Mars to see the next one presuming that Sir Clarke did his maths right (did he ever not?). On what day would that be?

You can listen to Sir Clarke read the story himself in the YouTube video 'Transit Of Earth' by Arthur C. Clarke read by himself. You can also listen here: http://recordbrother.typepad.com/imagesilike/files/transit_of_earth.mp3 and it seems download HMIcomposite_2Kx2K.mov from NASA here (though I haven't verified it yet): https://svs.gsfc.nasa.gov/vis/a000000/a003900/a003941/


texts: Why is it okay to watch a sunset but not an eclipse?

texts:
People watch sunsets all the time.  You don't see people using special "sunset glasses".

Yet with an eclipse, warnings are posted everywhere not to view it without special glasses.

Why is this?


texts: The relation of the lit side of the moon and the sun

texts: During different days when both the sun and the moon are seen I notice that the axis of the lit, illuminated, side of the moon does not pass through the sun there is some degree of diversion. Why?


texts: What is the orientation of planetary orbits?

texts:
I'm working on a planetary motion simulator. I've been working through the equations anomaly, eccentricity, etc. The one thing I'm curious about is if all the ellipses are oriented the exact same way (the direction of the periapsis of all planets are pointing the same way), or is it different for each planet?

What would this be called? I've only seen eccentricity and inclination.


texts:
Continuation of "Gravity on Mercury's highest elevation?"

Because when you Google that, you see "Caloris Montes" which is actually a mountain range consisting of mountains 1-2km tall from base to peak (Wikipedia). However, the previous question noted a value of 4.48 km "from what is considered a sea level". But mercury doesn't have sea, does it? Moreover, this value is confirmed here:

This new model reveals a variety of interesting topographic features,
as shown in the animation above, including Mercury’s highest and
lowest points. The highest point on Mercury is at 2.78 miles (4.48 km)
above Mercury’s average elevation, located just south of the equator
in some of Mercury’s oldest terrain.

A certain discrepancy is noted for our planet Earth. Mt. Everest is considered the tallest mountain (8848 m) when considered from sea-level. But, when we consider the height from base to peak, Mauna Kea/Loa is the highest mountain (of volcanic origin) (Total height=10.2 km, 4.2km above sea level). But, Mercury doesn't have "a sea level". So, why this discrepancy?
Questions:

What is the highest point of Mercury? Why is it "Calores Montes" even if it is a mountain range consisting of many mountains? Even if that peak of height 4.48 km is considered the highest point, why doesn't it have a name (since it is the tallest point, it should be notable and should have a name)?
What should be considered the base for planets which doesn't have a "sea" (sea level is only possible for Earth and Titan)? Wikipedia says " peak elevations above an equipotential surface or a reference ellipsoid could be used if enough data is available for the calculation, but this is often not the case". Where is it not applicable? Doesn't it lead to discrepancy like for instance, Mercury?

*This video says something called Mt. Hermes as the highest point of mercury.


texts: Convert MJD date range to number of days elapsed in IDL

texts:
Hopefully I'm in the appropriate section as my question is mainly about coding, but it's for astronomy.

Right now I'm trying to figure out how I can take a range of MJD values and convert them into number of days elapsed so I can normalize a plot of two supernova and their absolute magnitudes over time in IDL. Is there a simple conversion for this I'm not seeing or do I need to tediously convert every value to determine the number of days to use for my x-axis?

Note: I do not wish to convert to the date, but the actually number of days elapsed as to normalize my two plots for comparison.

Thanks!


texts: What's the reason the Astronomical twilight doesn't have constant time?

texts: What's the reason the Astronomical twilight doesn't have constant time although its degrees below the horizon (18 degrees) are constant?


texts: What makes the coming comet increase/decrease in brightness?

texts:
I understand C/1979 Atlas Y4 is potentially going to rapidly increase in brightness and visibility to the point we can see it very well in May-ish, in the Northern hemisphere.

I am wondering why it's not predictable whether or not it will, or what processes affect the brightness.  If it's simply reflection, why would it dim or brighten? I really don't think I understand comets.


texts: What's the easiest way to get 3D-positional data of galaxies

texts: Is there a database with cartesian coordinates (x, y, z) of galaxies? I only need positional data and calculating that using degrees and redshift for all galaxies could take a while and would be complicated.


texts: What will succeed the Arecibo Observatory?

texts: Just a few minutes ago, I got a notification from Space.com stating that the Arecibo Observatory will be, sadly, decommissioned due to extensive damage to its structure. So, with the loss of one of the world's largest telescopes, we will be put at a setback in space exploration and astronomy. So, what will succeed Arecibo and when will this happen?


texts: Whats the probability of a hazardous impact for human life on Mars?

texts:
Yesterday my sister and I have discussed the recent efforts of SpaceX to create a permanent colony on mars.

When coming to the several dangers of creating a habitat on a different planet, we got stuck on the probability of mars getting hit by an astronomical object thats large enough to wipe out life anywhere on the planet.
I assume the probability is higher than on Earth, due to Mars being closer to the Asteroid Belt, its size and thinner atmosphere. There are more potential objects to enter martian atmosphere and can be smaller than on Earth to create the same hazardous impact for life.

I have tried to research the numbers, but the only calculations I found were for specific asteroids and their probability to hit Mars.

On this StackExchange there are some questions concerningthe probability of an individual  (on earth) or a specific spot (on the moon) getting hit, but I found none for the hit of an object with a certain amount of impact (I hope thats the right word here).

So my question is:

What is the probability of an astronomical object hitting mars anywhere on its surface and kill all people currently living there?

Any impact destroying life-support systems and thus wiping out life on mars indirectly can also be included.

Assume that there is only one habitat, it is built directly on the surface and the first humans have arrived with the latest flight.

If there are any questions about the scope of this question, don't hesitate to ask.


texts: Does the Moon's magnetic field affect Earth's magnetic field?

texts:
I wanted to ask a question; it's simple but I cannot find any possible and perfect solution.

Earth has poles, North and South. By which we can get directions using a compass or a needle compass, but that's not the concern.

My Question:

Would the Moon cause a change in the magnetic field of Earth when they are interpassing or colliding with each other, as the Moon does come between the magnetic path of the Earth.

So would the Moon's magnetic field affect the Earth's magnetic field, just as its gravitational pull affects Earth's gravitational pull for oceans?


texts: Third rotational angle in equatorial coordinates

texts:
Right ascension and declination identify an object's position in the sky, but if we are looking at something through a telescope, there is a third angle of interest, namely how our view is rotated relative to the point we are looking at.
We could could think of this angle as a sort of celestial roll that goes with RA (yaw), and D (pitch).
Is there a standard name for this "roll" angle as a third element with RA and D?
What is its reference direction?  (Orthogonal to the direction given by RA and D, in the plane containing that direction and the north pole?)
And would increasing the angle turn our view clockwise, or counterclockwise?
Thanks,
Doguleez


texts: How to convert luminosity at rest frame wavelength of 1450 A to absolute magnitude at 1450 A?

texts:
How do I convert the luminosity (erg sec$^{-1}$ Hz$^{-1}$) of a quasar at a rest frame wavelength of 1450 Angstroms to absolute magnitude at the same wavelength?

I know that the bolometric luminosity is related to absolute magnitude via this relation from Bolometric magnitude:

$$M_{bol, ★} - M_{bol, ☉} = -2.5 log_{10} \left( \frac{L_★}{L_☉} \right)$$

Should the same relation be valid for the 1450 A rest frame luminosity and I just used that luminosity instead of the bolometric luminosity?


texts: What is the axial tilt of a planet measured relative to?

texts:
I am very much a beginner on the astronomy front but I understand about planets having different axial tilts, hence why Venus turns the opposite direction from the Earth and Uranus turns sideways.

However, I am confused as to what the axial tilt bearing is measured from. For example, if all planets were in a perfect line from the sun, would they spin perfect in alignment on their own various axial tilts? Would some still be 'off-set' by a few degrees to one side or the other?

Do we actually know please?


texts: I was wondering if the constellations visible from Earth would also be visible from Mars.  Would they look the same but just shifted slightly in the sky due to the larger circumference of the orbit?


texts:
My question is how do I convert a magnitude $K_S$, from a system like 2MASS, to $M_K$, and what are the differences. A use of this $M_K$ can be seen on Delfosse et al. (2000) in the $\log(M/M\odot) - M_K$ can be found. In the end I want to be able to use a $K_S$, and other possible parameters to derive the mass of the star.

Delfosse et al. (2000) - Delfosse, X., Forveille, T., Ségransan, D., et al. 2000, A&A, 364, 217


texts:
What's the definitive source for names of geographic objects on the moon?

Reason: As a computer graphics project I've rendered a scene based on LROC terrain data. I want to know what I'm looking at.

The most detailed atlas I can find online is this one:

http://planetarynames.wr.usgs.gov/Page/Moon1to1MAtlas

...but it's not brilliant and there are lots of small but prominent craters and ridges which aren't labelled. It may be the some of these simply don't have names, but it's also plausible that there are simply too many to list in that atlas. How can I find out for sure?


texts: Does the Hubble constant depend on redshift?

texts: I know there are lot of questions on the Hubble constant already, but I am curious to know if it changes with redshift? If at current redshift, $z=0$, we know its value to be 0.7, will it be different at higher redshift ($z=0.1$)? If so, is there any relationship with redshift?


texts: Will comet 21P that just passed Earth on Sept 10 produce Draconid storm on Oct 9?

texts:
Comet 21P/Giaccobini-Zinner just made its closest pass to Earth and also made its Solar perihelion on the same day (Sept 10) which is roughly one month ahead of the annual Draconids meteor shower (Oct 9).  In both 1933 and 1946 these same circumstances also occurred and there were reportedly 1000s of meteors per hour in those years - meteor storms.

Question - I know the expert forecasts are not calling for more than 20 or so per hour based on some reference data about debris streams, but is there any chance that they may be wrong this year in their forecasts? Could the favorable circumstances this year plus a new debris stream result in a meteor storm surprise next week?


texts:
Hot Jupiters are giant planets that are very close to their host star.
How many Hot Jupiter exoplanets have been found around stars more massive than our Sun?

Has the number of Hot Jupiters discovered as a function of host star mass been plotted? Say $x$ Hot Jupiters around stars that are 1 to 1.5 solar masses ; $y$ Hot Jupiters around stars that are 1.5 to 2 solar masses,...


texts: Is the longitude assigned to sunspots spherical or projected?

texts:
Sunspot maps are created from a projection of the sun, so the coordinates of sunspots (or active regions in general) are assigned according to it.

Do these coordinates correspond to actual spherical positions, or are they altered as a result of the projection?

Edit: After seeing the answer, I realized that a part of what I am asking about was not clear in the initial question. So here it is: Are the values of the sunspot coordinates as provided officially in spherical positions or in projection?

A commonly used instance of "official" records is X-ray measurements from the NOAA GOES. The text files are found here.

For example, see file for 2000. The output is documented here, under "Output File Specification".


texts: Fingers of God effect for galaxy clusters

texts:
Galaxies that reside in galaxy clusters are know to have peculiar velocities that cause the Fingers of God effect.

But what about galaxy clusters themselves?

Do they also have peculiar velocites by interacting with other galaxy clusters?

If so, are they high enough to be taken into account or low enough to be ignored?


texts: How can I validate star names and designations?

texts:
While most star names and alphanumeric designations I've seen appear to be pure alphanumeric plus space, I have seen designations with both - and + characters in them too.
Is there a reference or standard anywhere for what characters are valid for designations and star names?
I've had a look around for this information, but I can't find any references which would allow me to write a comprehensive BNF syntax or a regular expression to parse and/or validate star names and designations.
In particular for a project I'm working researching, I would like to know if either a , comma or a | pipe character has or might ever be used in a star name or designation.


texts: Relation between absolute magnitude of UV and star formation rate

texts:
I surfed the internet and searched a lot of sites,
so far I got this

but unable to find the formula which relates only Muv and the Ψ as I don't know the value of parameters Auv and μ(z).
If there exists any such formula, then do help!


texts:
There has been research that suggests that the changing brightness of Brown Dwarves are due to bands of Iron/Silicate clouds. Several models have been made that supports that hypothesis. My question is: Which part of the model are the actual clouds? Are the clouds the bright orange bits? Or are those bright areas “breaks” in the clouds and a view of the Brown Dwarf below.

5 MB animated GIF: Brown Dwarf Cloud Model


texts:
How does Mars surface compare to Earth's surface? Mars is quite smaller than Earth, but most Earth's surface is covered with water. I thought making the math could be relatively easy but Earth isnt a sphere and I dont know about Mars?

What's the proportion of Mars' surface compared to Earth's surface uncovered of water?


texts: Is it possible to see Saturn from Titan's surface, day and night?

texts:
Titan is the only moon in our solar system with a thick atmosphere, similar to what our Earth's atmosphere was before life "appeared". It also orbits Saturn close enough to actually see it beautifully in the sky... or can it?

Titan has a very thick and hazy atmosphere. Tholin seems to be the main factor of this "haziness". Also we can't see Titan's surface from space without infrared instruments. So in visible light, Titan looks like an almost uniform ball of beige, yellowish, golden brown because of its atmosphere, hiding the surface below.

So this should probably be the same case the other way around, right? Can we see Saturn from the surface of Titan, or does the haziness hide the parent planet from view during day time and night time (since I believe the atmosphere's opacity changes in day time and night time)?


texts: Strange bright light in the sky flying fast

texts: I was out with my dad on our porch watching the stars with our telescope. after awhile of looking and taking pictures I noticed something strange in the sky. There were two airplanes flying close to each other, but next to those two airplanes was a very bright light (see how the stars are bright? Well that one was a lot bigger and I lot brighter, and to give you an example it was moving as fast as the planes, I showed my dad and he as well saw it, so I knew I wasn’t dreaming, it wasn’t moving straight either, both me and my dad could see it was going in zigzags, not a straight line, it desapeared after awhile behind he trees, we didn’t get to look at it through the telescope since it was moving so fast...what could it be...? Both me and my dad agree it was going as fast as the planes next to it, it was brighter then both the planes and the stars and it could not have been a third plane since broth planes were just so small and it looked like a very big star. FINALY it was not moving in a straight line...so the what would it be...?


texts: In the JPL small body browser, why is uncertainty on absolute magnitude "N/A"?

texts: In the JPL small body browser, orbital elements are all provided with uncertainties and even a covariance matrix, such as for 2013 LA2.  Very good.  But underneath, the absolute magnitude is reported with a sigma of "n/a".  Why would the uncertainty for an absolute magnitude be not applicable?  Is it not a measurement but somehow given by definition?


texts:
This is an exercise from a text, I’m learning from and I can’t understand it so I’m asking just to develop my knowledge:

The explosion of V603 Aql (Nova Aquilae) took place in June 1918. The nova reached maximum brightness -1.1 mag. The nova's spectrum was observed to shift absorption lines corresponding to a radial speed of 1700 km/s. In 1926, a weak envelope was observed around the nova with an angle of 16''.
Determine the distance and absolute brightness at maximum for V603 Aql.


texts: Would this effect occur if an ice planet was put into orbit or trajectory?

texts:
Imagine an earth getting warmer. Humans decide to make their homes ready for a voluntary ice age. All the space agencies work together to get an icy planet/moon into our orbit between us and the sun.

My theory is that because the sun is heating up the ice and blowing it in the direction of earth, it'll make the Earth colder.

That final part is my question: Could ice molten in space eventually reach earth and perhaps be pushed in that direction by its heat?? Not taking into account whether or not it would benefit the earth.

I'm an amateur with no knowledge of physics, chemistry and astrology and want to learn answers to my questions.

Thanks in advance!


texts: How to read 5 degree data of green line intensity

texts:
When I open the 5 degree data of Green Coronal Emission line from this, I get a weird table which is not simple like the one for Coronal Index. I am only providing the table for 1939.

http://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-indices/solar_corona/5-degree-data/data/1939/1939

I can't provide the link for the formats used due to the restriction (max of 2 links until I have a rep above 10) but it's in the folder for 5 degree data.

I searched extensively connecting the formats (like I4, I2) to the datasheet but couldn't even scratch the surface of it.

I want the data for green coronal intensities and positional degrees in that respective year but can't find from this table. How do I find them?


texts: What is the difference between gas and dust in astronomy?

texts:
Is there a strict difference between gas and dust?
In Earthly environment most things become gaseous if heated enough. The temperature of interstellar medium seems to range mostly between 10 and 10 000 Kelvin. Is gas/dust an analog for hot/cold, or does the phase diagram of the element in question matter too? Can metals and molecules be gas in astronomical terms?


texts: Have parameters been determined for the Fourier components of a Milky Way spiral density-potential model?

texts:
Spiral arms in galaxies can be modeled by potentials of the form
$$\Phi_{\text{spiral}}(R,\theta,z,t)=\sum_mA_m(R,z)\cos(m\theta-m\theta_0-\phi_m(R)-\Omega_pt)$$
where $A_m(R,z)$ is the $m$th-order coefficient based on some potential - such as a Miyamoto-Nagai potential - $\phi_m(R)$ is a function typically of the form
$$\phi_m(R)=\alpha_m\ln (R/R_{0,m})$$
for some characteristic radius $R$, and $\Omega_p$ is some pattern speed. I've read that typically the $m=0$ component dominates, followed by the $m=2$ term. There may also be an $m=4$ term, though it is typically weaker.

This model describes the disk component of a galaxy with two main spiral arms. The spiral arms of the Milky Way are more complicated; some consider it to have two major arms and two more subordinate arms, while others consider it to have four major arms.

Have any potential or density models of the Milky Way been created using these Fourier components, and if so, what are the parameters used (the $m$s, $A_m$s, $\phi_m$s, and $R_{0,m}$s)?


texts: Will I be able to see the Leonid Meteor Shower during mid night?

texts:
Most of the articles online say that the peak will be in a couple of days and around 2:00 AM in the night. I am currently living in Dubai, UAE.

When I use Google Sky Maps, it shows both the Leonids Meteor Shower and Leo Constellation below the horizon, when using the search feature. It only comes above the horizon at around 6:00 AM, when it is 45 minutes since sun rise.

So, I am not sure whether it'd be dark enough to see them. What is my best course of action.

EDIT:
This link: https://www.timeanddate.com/astronomy/meteor-shower/leonids.html shows Leonids will appear at 65° Azimuth and 1.7° altitude. How'd I interpret that?


texts: What constellation is closest to the Zenith with RA=12 and Dec =47.6?

texts:
I have several options, but I do not know how to calculate which option is closest to the zenith in title. Could you please help me with this? Thank you.

Canes Venatici,CVN,13.14763.+40.04187,M
Cygnus,CYG,20.61006,+42.53633,A
Lynx,LYN,8.01440,+46.23233,M
Perseus,PER,3.49832,+43.88451,A
Ursa Major,UMA,10.98253,+52.52900,A


texts: Why do most meteors vanish just before hitting the ground?

texts:
Many times we see in the sky that most of the meteor shower trails vanish when they are about to strike the earth several feet above the ground. Why does this happen? They could strike the earth's surface (still emitting light until they strike).

Pic source: http://imgur.com/afiZGCm


texts: How likely is it that the Sun will destroy our electric society?

texts: Given the studies of the Sun and similar stars and the most impressive understanding of its physics, is there any kind of probability distribution for its dangerous behavior? There are also some historic data about events in 1859 and 775. What is the estimated probability of solar activity destroying our electric grid within this century?


texts: Are galaxies moving in each direction with same speed?

texts:
All galaxies are moving away from each other (us) because of the expansion of the universe.

Are they moving with same speed in each direction?


texts: So we've seen millions of galaxies, and all of them have a bright, yellow nucleus. What is the cause of the yellowness? Is it because of aging stars, redshift from the SMBH, or something else?


texts: How can I know the source size using the spectrum variability?

texts:
When reading some astrophysical papers I saw things like this:

The sources are variable on very short timescales, implying a compact emission region.

How can we conclude or measure the source size, or emission region size (or its compactness) from the variability of the spectrum?


texts: What are the raisons d'être for the Large Binocular Telescope "binocularity"?

texts:
edit: The short form of the question is Why are there TWO telescopes?? A longer version follows.

The Large Binocular Telescope (and LBT blog as source of images below) has two 8.4 meter diameter mirrors, allowing for the possibility of interference in one dimension.

I'm aware that a single baseline, two-element stellar interferometer can be used to measure the separation between a pair of stars by looking at the Fourier transform of the intensity vs time of the interference. A single frequency peak is produced by one star, but if there are two close together, there will be "beating" in the time series that shows up as two peaks in the FT.

But I'm wondering if the LBT was designed and built with a plan to do more than that. Just for example, did plans include an ability to use interferometry to help reconstruct 2D images, or enhance the resolution beyond that which is already provided by the adaptive optics used in each half separately? Were there other plans or justifications?

Possibly helpful; Current Status of the Facility Instrumentation Suite at The Large Binocular Telescope Observatory

Open image in new window for full size:


texts: Why does the number of extrasolar planets vary in different sources?

texts:
There are at least three catalogues that are counting up-to-date discovered exoplanets. What criteria do they use to count the number of planets? Every catalogue has a different count value.

So at this moment various catalogues as:

exoplanet.eu
Open exoplanet catalogue
NASA exoplanet archive
etc.

show values of confirmed number of exoplanets between approx. 3500 and 4050.

Why do they disagree with each other?


texts:
Someone asked me this question:

  To see the color of the Great Nebula in Orion, how large the aperture of the telescope should be.

I don’t even know whether this is possible. I understand that the colorful patterns of the nebulae are from the cameras. Besides, my own experience shows that when I target the telescope at them, I see nothing but some white blur.

So is this possible when we watch the deep sky objects with a really huge telescope, under the finest conditions?


texts:
Is it possible that meteoroids, comets, asteroids or other small bodies from around a nearby star (such as Alpha Centauri) could get into the solar system?

How low is that possibility?

Edit:

Since the Oort Cloud is not being gravitationally attracted enough to the Sun to form a disk, I assume this is the same for Alpha Centauri's Oort cloud. Therefore, my question is: can the Sun gravitationally pull a comet from Alpha Centauri's Oort cloud?


texts: If the earth lost 1/81th of its mass how would it orbit change?

texts:
If a planet becomes lighter, then I believe its orbit will change.

For example, the moon is 1/81 of the mass of the earth. So, if the moon disappeared, then the earth-moon system would lose 1/81th of its mass. How would the orbit of the earth change in that circumstance?


texts: Why don't storms on gas giants move to the poles, like hurricanes on Earth do?

texts: On Earth, hurricanes usually move from the equator to the poles. But if you look at a picture of Jupiter, you'd see that the Great Red Spot isn't anywhere near the poles. So the question is: why don't storms on gas giants move to the poles like storms on Earth do?


texts: Are the "extinct species" of meteorites originally from the "Barbarian" asteroids?

texts:
I've asked earlierin this unanswered question about an "extinct species" of meteorite, now I've just read in Phys.org about Barbarian asteroids:

  Named after the first asteroid of this type discovered, Barbara (234), Barbarians are a key to understanding how the solar system first formed. Barbarians are extremely rare and ancient, and were present before the Earth was created. Only 13 Barbarians have ever been discovered.

Are these two different types of extremely rare materials, or are the "extinct" meteorites actually products of the "rare Barbarian" asteroids?

From: UWA Zadko Telescope helps reconstruct 'Barbarian' asteroids.


texts: How can a very old star be formed among Population III stars?

texts:
After looking at some articles about old stars, (this, that, and this Wikipedia article), I thought about how such an old and small star could have formed. As the early universe had very massive, early-type stars and (no? almost none?) smaller, late-type stars. So how could a ~$1M_\odot$ star have formed in the early universe, where massive Population III stars dominated?
Here are my theories, if you may find them helpful.
Mass loss via a long-dead companion
Star Foo and Star Bar are both $300 M_\odot$ stars closely orbiting each other. Star Bar is slightly more massive than Star Foo, causing Star Foo to lose mass to Star Bar. Now, Star Bar is $580 M_\odot$ and Star Foo is now drained to $20 M_\odot$. As Star Bar ages and becomes a supergiant, Star Foo gets engulfed by Star Bar, reducing Foo's mass to $\text{1-2} M_\odot$. Star Bar then goes supernova, ejecting Star Foo. 13 billion years later, Star Foo ages and becomes a subgiant, what we see today.
Formed in a massive star's disk
When the universe was young, there were plenty of materials to create stars. One massive star, star Foo, formed. It had a vast disk of gaseous material, weighing over $2 M_\odot$. In the disk, perturbations caused a massive clump of gas to form together, causing the ignition of hydrogen and creating a small, yellow dwarf of mass $0.8 M_\odot$, called star Bar. When Foo went supernova, Bar was ejected. 13 billion years later, we see an ultra-metal poor, very old, late-G type borderline-subgiant.
Split off from a massive star's envelope
A massive star forming region creates a star, Foo. Foo is very massive and large, and begins losing mass through the stellar wind. In a massive eruption, over $1 M_\odot$ is ejected from the star's envelope. This gas clump collapses under its own weight to form a small, Sun-like star. As the universe ages, we see a metal-poor, very old red giant.


texts: Cosmic variance - Fourier Transform - a few precisions

texts:
I have posted initially on physics exchange but none answer, so I try my chance here (I am going to delete the physics exchange one) :
I cite an original report of a colleague :

If we are interested in power spectrum, we want to estimate the
variance of the amplitude of the modes $\mathrm{k}$ of our Fourier
decomposition. If one observes the whole observable Universe and we
do the Fourier transformation we get a cube whose center is the mode
$ |\vec{k}| = 0$ which corresponds to the mean value of the observed
field.
This mode has only one pixel. How do we measure the variance of the
process at $ |\vec{k}| = 0 $? We can not.
In fact we can but the value of doesn't mean anything because the
error is infinite. In other words, we have an intrinsic (statistical)
error which depends on the number of achievements to which we have
access.
one will be able to consider spheres of sizes $ dk $ between $ [k: k +
> dk] $ which will contain a number of pixels $ N_ {k} = V_ {k}/(dk)^{3}$ where $ V_{k} = 4 \pi k^{2} dk $ is the volume of the sphere
and $ (dk)^{3} $ is the volume of a pixel in our Fourier transform
cube.
So one can estimate how many values one can use to calculate our
power spectrum for each value of $ k $. The greater the $ k $, the
greater the number of accessible values and therefore the statistical
error decreases. The power spectrum is a variance estimator so the
statistical error is basically a relative error:
$ \dfrac{\sigma (P(k))}{P(k)} = \sqrt{\dfrac{2}{N_{k}
> -1}}_{\text{with}} N_{k} \approx 4\pi \left (\dfrac{k}{dk}\right)^{2} $
So we can see that for the case $|\vec{k}| = 0$ we have an infinite error because $N_{k} = 1$

I can't manage to proove that the statistical error is formulated like :

$\dfrac{\sigma (P (k))}{P(k)} = \sqrt{\dfrac {2}{N_{k} -1}}_{\text{with}} N_{k} \approx 4\pi \left(\dfrac{k}{dk}\right)^{2}$
and why it is considered like a relative error ?

Which are the conditions to assimilate a statistical error (standard deviation) to a relative error ($\dfrac{\Delta x}{x}$) ?

How to prove that $N_{k} = 1$ in the case $|\vec{k}| = 0$ ?

Any help is welcome.


texts: Hamiltonian of general three body problem

texts:
i try to extend my analysis from planar restricted three body problem to the general one.

Is there anyone that can help me to find out the Hamiltonian for this prolem in cartesian coordinates?

I need the hamiltonian of 3D case somethink like eq.(1) in this article or in this one paper again eq.1 . Because my symplectic integrator can be used only if I have the fixed cartesian coordinates.

Thanks


texts: If all stars rotate, why was there a theory developed that requires non-rotating stars?

texts:
According to Penrose's research, a non-rotating star would end up, after gravitational collapse, as a perfectly spherical black hole. However, every star in the universe has some kind of angular momentum.

Why even bother doing that research if that won't ever happen in the universe and does it have any implications for the future of astrophysics?


texts: How does the number in stellar classification indicate properties within the range of that class?

texts:
I am doing some research for a video game and I wanted to store stellar data on a star, such as its Stellar Classification, and then from that derive a physical appearance in the game.  These are fictional stars.

My original thought had been to store the star's classification, For example G2V and then at runtime I could use that data to determine things like surface temperature, brightness, radius, and mass.  From temperature I can also derive color.

However when I sat down to start coding a first pass on this I noticed something that confused me.

According to Wikipedia, our Sun, Sol, is a G2V star.  The number is supposed to indicate a "sub" classification.  A G2 star would be 20% between a G star and a K star.  A table there lists a G type star as having a surface temperature between 5,200 K and 6,000 K.  Therefore I figured a G2 star would have a temperature of about (I know nothing here is EXACT) 5,360 K (20% of the way between 5,200 and 6,000) but apparently it actually has a temperature of 5,800 K which is about 75% between the given range.  So why is Sol not a G7 of G8 star?

And then once I hit that irregularity, I had to assume that things like Radius and Mass are probably also not linearly interpolated along the range.

Is there a feasible way to derive properties such as I am looking at based on the Stellar Classification?


texts: A double star consists of two stars of equal brightness at equal distance from the Earth. What is the apparent magnitude of the combined object?

texts:
The magnitude of each star in the V-band is mV= 8.34. If these stars are so close together that they appear as one object, what is the apparent magnitude of the combined object?
I just want someone to point me in a general direction of how to approach this problem. The magnitude is logarithmic so it won't be double when combined. Or at least that is what I think. How do I apply the formula
$$m=-2.75 \log_{10} F + C$$


texts: If Mars were tidally locked to the Sun, what would the temperatures on its surface be like?

texts:
Since there's very little atmosphere on Mars, it doesn't matter much whether the Sun is in the zenith or hanging just above the horizon: without the atmospheric "filter," the sunlight would have roughly the same effect on all sunlight areas.

What would the temperatures be like on the sunlit portion of the planet?


texts: Is the sphere of influence of our milky way's center super massive black hole same as the Milky way's radius?

texts: The sphere of influence is a region around a supermassive black hole in which the gravitational potential of the black hole dominates the gravitational potential of the host galaxy(found it in wiki). So is it the same? If not, what holds the milky way together?


texts: What Is The Maximum Distance Our Finest Instruments Could See When They're Perfected?

texts: Radius of the observable universe is 47.5 billion light years,which means we are seeing things which are about 48 billion light years away. At a rough estimate,at what distance would our finest instruments and telescopes be unable to see or detect anything at all,& is there anything in the idea that if we were able to see far enough,we might see our own galaxy as it appears from an immense distance,its light having circled the universe? And as space is not a perfect vacuum,wouldn't the light be significantly retarded by the end of such a long journey?


texts: Have there been studies of "old photons" to see just how constant things like Planck constant has been?

texts:
The question Are photons aged? and answers therein have got me thinking:

I vaguely remember hearing something about experiments where "old photons" were collected by large telescopes from very distant objects, and either their energies or their frequencies were compared to their wavelengths to check the (linear or inverse) some fundamental constants, perhaps those used in:

$$E = hf = h \frac{c}{\lambda}$$

Questions:

Am I misremembering, or has this been done?
What were the results and to what level of precision was non-variation constrained?


texts:
As far as I can tell when the Voyagers listen to Earth they have the Sun in the same beam. I never did calculate how bright a blackbody Sun would be because I have no idea if that's representative of the Sun's output in S-band

How well can Voyager 1 separate Earth signals from Solar noise these days? shows that the Voyagers see the Sun and Earth separated by 0.2 to 0.5 degrees each year.

I also don't know how wide of a slice in frequency the front end is exposed to, or if the Sun would be strong enough to saturate it.Frequency responses of Voyager's S-band high gain antenna's feed-horn and receiver front end & IF? remains unanswered.
This is related Why is the operating temperature for the Voyagers' receiver noise calculation about 1550K? and answers there are informative.
I assume the designers were optimistic that Voyager might survive this long and designed the system to be able to pick out transmissions from Earth from the Sun's output, but I'm not quite able to put the whole puzzle together yet.
So I'd like to ask:
Question: How bright is the Sun in S-band? Is there a measured value for power per unit frequency? How close is it to what a blackbody would produce at say 5800 K? At this frequency is there a big difference between when the sun is quiet and when it is active?
See also Do stars have "radio photospheres"? Are they different from their optical photospheres?
note: The linked questions and answers have a lot of Voyager-specific information which is relevant to Voyager's operation in S-band, but I have nothing on the Sun's behavior at 2.1 GHz Actually the first link gives the downlink frequency as

2113.312500 MHz for Voyager 2


texts: In the Inflation theory, it said that the Inflationary epoch has happened $10^{-32} \,\mathrm{s}$ after the Big Bang, and I cannot find anything related to how this number was calculated and how accurate was it. Thank you in advance.


texts: Equilibrium Temperature for Extremely Cold Planets: Incorporating the CMB and Intrinsic Radiation

texts:
I want to check if I'm doing this right. I'm computing the equilibrium temperature for planets where the CMB and/or the planet's intrinsic radiation (as in weakly radiating jovians) matters.
I start with the commonly quoted
$$4\pi\sigma R^2 T^4=\frac{\pi R^2L(1-a)}{4\pi d^2}$$
I note that the left side corresponds to outflux, and the right side corresponds to influx. It follows that we can add absorbed CMB $4\pi\sigma R^2 T_{\text{CMB}}^4(1-a)$ to the right side. We add intrinsic flux $L_{\text{self}}$ to the right side also, because it is equal to outflux when the star and the CMB are absent. So we have:
$$4\pi\sigma R^2 T^4=\frac{\pi R^2L(1-a)}{4\pi d^2}+4\pi\sigma R^2 T_{\text{CMB}}^4(1-a) + L_{\text{self}}$$
And the ultimate expression isolating $T^4$ is
$$T^4 = \frac{L(1-a)}{16\pi\sigma  d^2}+T_{\text{CMB}}^4(1-a)+\frac{L_{\text{self}}}{4\pi\sigma R^2}$$
Right?


texts: Roche limit - calculation with centrifugal forces

texts:
Let's assume there is a small natural satellite oribiting a massive planet. The satellite rotates synchronously (revolution period = orbital period) on a circular orbit, both bodies are homogenous and rigid. The question is, how to find the Roche limit with regard to centrifugal forces?

With use of Wikipedia I understand that the Roche limit is basically the orbit where difference of gravitational forces between the planet and two points in the satellite body (its centre and a surface facing to the planet) cancels the gravitational pull of the surface of the satellite to its centre. Wikipedia also states that more accurate is to include also the centrifugal force on the surface of the satellite due to its rotation.

Why is not included the difference of the centrifugal forces acting on satellite centre and surface facing to the planet, caused by satellite's orbital movement?

Are there any other forces I need to take into account, for example orbit of the whole sytem around a star?


texts: Find a planet with incomplete information of a star chart

texts:
I am wondering why it was so hard to locate Luke in Star Was Episode 7, if you already have the small part of the map.

Suppose we have a sector of our galaxy that roughly equals the one missing in this image. (I found no image on the web of the part in question. In the movie version on netflix you can take good look at it at 52:56.)

Is it possible and how hard would it be to identify a planet within that part of the map, given our knowledge of our galaxy and

we only know the small part and have no information about its size.
there might be "landmarks" (planets, stars, nebulars, and the like) missing.

If it is not possible, what minimum requirements would have to be met (on the available equipment, the map, our knowledge, ..) to make it possible?

Please note: this is not a Star Wars question, that is just the motivation.

About which galaxies do we have enough knowledge to be able to do this?

http://ko.starwars.wikia.com/wiki/%EC%9D%80%ED%95%98%EA%B3%84?file=TFA_galaxy_map.jpg


texts: Determining observer's position based on azimuth and elevation of observed object

texts:
It is possible to generate Ephemeris through the web-interface of JPL's Horizon system based on observer's location. Unfortunately I don't know the formula that is used to do that with a high precision but I'd like to reverse this action.

Having Azimuth and Elevation of The Moon at a certain date and time, I'd like to know the observer's location. Where do I even start?


texts:
Why are planets moving in the first place? Gravity causes them to orbit, but why move at all?

note: this is not a question on why planets orbit each other, I know the reason for that is gravity. What I'm asking is why do planets move at all? For example, if you turned off gravity, why would the planets carry on moving apart rather than be stationary?


texts: Terminology: planet plus atmosphere vs planet and atmosphere as separate things

texts: When discussing a rocky planet, is there any terminology to distinguish that you're talking about the whole thing, including the atmosphere, veruses that you're talking about the ocean + crust + mantle + core as a separate thing from the atmosphere?  Or do you have to depend upon context to make that distinction?


texts: How is the Sun tilted to its orbit around the Milky Way's center?

texts: We know how the Sun is tilted in reference to its planets but how is it tilted to Sagittarius A or its orbit around it? Or isn't it tilted at all?


texts: Image sets for testing stacking algorithms?

texts:
I am looking for sets of astronomical images for testing different kinds of stacking algorithms.

The idea is simple: if one has $N$ images of the same object, the signal-to-noise ratio of the averaged image increases with $\sqrt{N}$ under certain conditions.

Where could I obtain data for testing?

PS. I would propose adding the tags "image", "ccd", "research", "signal processing", and "machine learning".


texts: Where do we define the "surface" of a gas planet?

texts:
Since gas giant consist of most gas components, where do we establish their "surface"?
My take is basically to take the limit in which all light is opaque. For example, in this photo:

The surface, then, will be the limit of the black blackground with the planet.
Any other way to formally define the "surface" of a gas giant?


texts: Can you create a black hole using kinetic energy?

texts: Imagine you have a particle accelerator that you can crank up to arbitrarily high energies.  Because of General Relativity, the particles get heavier and heavier as you dump more energy into them.  Will these particles ever become a black hole from this relativistic mass?  If so, what will an observer particle moving parallel to the black hole, just below that speed, see?  What I'm getting at is, kinetic energy is relative.  So therefore relativistic mass is as well.  So would these particles be black holes to some observers but not others?


texts: Adverse effects of urban growth on old astronomy observatories? Need article/book

texts:
I am looking to get some information on the adverse effects of urban growth/light pollution on the oldest/traditional observatories of the world (europe).

Can anyone recommend me books or articles to read?


texts:
I've been reading the book Planetary Geology. In chapter 7, section 7.6, the author states that

The angle of incidence at which asteroids or comets encounter the surface of
a planetary body follows a Gaussian probability distribution with vertical and
horizontal collisions being extremely unlikely and the highest probability existing
for 45°

Why is this the case? Why doesn't the angle of incidence for meteoroids follow a uniform law? Isn't there just as much chance for an asteroid or a comet to arrive from any direction?


texts: How many quakes have been detected by InSight?

texts:
Insight has been on Mars with its seismometer for almost two years now. Has it detected any mars-quakes yet? How often do these quakes seem to occur?
Is there a website where the current number of quakes detected by insight is indicated?


texts: How come moon's difference in thickness between sides does not create an unbalance on its mass?

texts:
I've just found out that moon's dark side is 30 miles thicker then the closer side to the Earth. So I'm wondering about moon's mass. How come it's still balanced? Supposing the far side is indeed heavier, considering More Mass More Gravity, wouldn't it have to be closer to Earth?

Sorry if I'm making stupid assumptions, I'm just a curious fela.


texts: Maximum disturbance to space time of gravitational waves, and will this affect humans?

texts: Do we have a theory that can tell us how much change gravitational waves can make to space time. If it is infinite then I think any time we can see biggest change in space time and how much could it affect to humans?


texts: Converting an RGB image to fits (astropy)

texts:
I am trying to save a NumPy RGB array (a 3d array with dimension 512x512x3), to a .fits file using astropy.io.
Saving this array to a .png file works fine, but when I'm trying to save it to a .fits file using HDUList.writeto, it produces just garbage colors.
Also, I have to reshape the image like so:

img = img.reshape(img.shape[2], img.shape[0], img.shape[1])

or it will try to store just 3 column of the image instead of 512.

Each element in the 3d array contains a value between 0 and 255.


texts: Why does M101 search string have RA variable from 0 to 360 and Dec variable from -90 to +90 in the Hubble Legacy Archive?

texts:
I was scraping some images off the Hubble Legacy Archive and I found that searching M101 with RA in range 0-360 and Dec in range -90 to +90 yields results. Now I understand that Messier 101 galaxy has the co-ordinates RA 14h 3m 13s | Dec +54° 20′ 57″.
So what images am I getting if HLA has images for M101  RA = 52.000000  Dec = -13.000000  r = 1  [03:28:00.000 -13:00:00.00]
Could someone explain what's going on?


texts: Exactly what in Saturn has been located to within 4 km precision?

texts:
Saturn has been located with fantastic precision thanks to Cassini and VLBI. The location of the 120,000 km diameter giant planet (when defining the 1 bar pressure level as its surface) is known to within 4 kilometers. This has already been helpful in the (preliminary) discovery and characterization of "planet nine".

I suppose it is the Saturn system's barycenter which has been located gravitationally. At this level of precision I suppose that the moons', especially Titan's tidal effects must be considered. But also Saturn's flattened shape and maybe even weather systems. Saturn is known to be lumpy inside, this has been discovered by the effects it has on the inner rings. Such lumps have similar effects as a moon, so I wonder if these too are being considered at the 4 km precision level, and overall exactly how the point located is defined?


texts: What would the pressure and temperature of gas be, right above Jupiter's gas/liquid boundary?

texts:
Older pages like this "Exploration of the Solar System" course page describe the transition as being a few hundred kilometers down.

More recent findings seem to put the boundary deeper. See

  The result was a surprise for the Juno science team because it indicated that the weather layer of Jupiter was more massive, extending much deeper than previously expected. The Jovian weather layer, from its very top to a depth of 1,900 miles (3,000 kilometers), contains about one percent of Jupiter’s mass (about 3 Earth masses).

- nasa.gov, March 7, 2018: "NASA Juno Findings - Jupiter’s Jet-Streams Are Unearthly"

and

  Below whirling jet streams, 3,000 kilometres deep, lies a dense, rotating core of liquid hydrogen and helium.

- abc.net.au, March 7, 2018: "Jupiter: Juno uncovers deep jet streams, dense liquid core — and cyclone mystery"

Given the updated understanding of the mass of gas above it, what would the pressure and temperature be at that level?


texts: Is it correct to say that only binary and solitary star systems are stable?

texts: Recently it has been shown that a large number of binary stellar systems exist.  It seems to me that the orbits of stars in systems containing three or more stars will inevitably be chaotic, resulting in either mergers or ejections.  Binary stellar systems, though, are effectively stable (neglecting the very slow decay of orbits due to gravitational radiation and perhaps tidal interactions).  So, it seems that in the long run we should expect most stellar systems to be either binary or solitary; the first due to ejection (eventually) of all but two of the stars from a multi-stellar system, and the second due to the ejection of single stars from multi-stellar systems.  Is this correct?


texts: Are there predictions of the distribution of matter at the end of time

texts:
Are there any theoretical predictions or "educated speculation" by cosmologists on how matter will be distributed at very, very distant times in the future?

For example, will matter be:

agglutinated into a big cold ball?
diluted across the universe in tiny bits?
large clusters of matter here and there?
something else?


texts: Where and when will someone on Earth be standing with the floor parallel to the Ecliptic plane?

texts: I have been trying to figure this out and I think the answer might be - once per day for anyone living on the Tropic of Cancer or Capricorn. Is that right? To be clear - I want to know where on Earth and when/how often a person standing upright will be standing with the floor parallel to the ecliptic plane? Thank you for your help!


texts: What is the reason for that scale? Is it because otherwise defining an maximum would be too hard(?). Why do objects that are (apparently) brighter get assigned a smaller number (and down to negative)?


texts: What are the units of distance in this subtended angle calculation?

texts:
I'd like to find the distance at which a 2.4 cm coin is subtended by an angle of 10". I've drawn my diagram and found that $D=\dfrac{d}{\alpha}$ using the small angle approximation. Since $10" = 4.85\times10^{-5}$ rad then $ D = \dfrac{2.4 \times 10^{-2} m}{4.85 \times 10^{-5}rad} = 495$

Are the units of distance in this calculation meters? In other words why would the units of radians be 'dropped'?


texts: How wary should I be of old cosmology books?

texts:
Recently I bought a couple of books on cosmology from a second-hand bookshop. One was published in 1993 and the other is from the 1970.

I know, from a recent book, that the inflaton theory is probably newer than both books and that the Higgs Boson has been discovered, but that is all that I know has changed recently in the field of cosmology. Has anything else changed since then?

Which topics of the books should I understand are considered outdated?

The two books are Modern Cosmology by Jagjit Singh (published 1961 and rereleased in 1970) and Afterglow of Creation by Marcus Chown (published in 1993)


texts: How far is the nearest black hole from our solar system? Is there an official list?

texts: Which is the nearest known or suspected black hole from our solar system and how far is it from us? Is there an easily-viewed catalog that astronomers use to keep track of these?


texts: Computationally intensive technique to search for TNO's within the noise of historical photographic data?

texts:
I remember reading recently about a technique to search through lots of old survey images to try to identify trans-Neptunian objects that were so dim that they were "lost in the noise" in single exposures and so have here-to-fore escaped detection.
This was a few months ago I think, but now I can not remember where or exactly when.
From what I remember it was a computationally intensive technique where images were effectively overlayed with offsets determined by hypothetical test orbits. In other words suppose a field is photographed one a year for 10 years. 1 or 2 sigma noise-like dots of diffraction-limited size will be ignored in any one image, but if many of them show dots that overlap when images are shifted by 0.126 degrees per year, then this may be due to a real TNO at 200 AU. ($\text{1 year} \times (\text{180} / \pi) \times \sqrt{GM/a^3}$)
Question: What was this computationally intensive technique to search for TNO's within the noise of historical photographic data that I'm remembering? Where was it recently published or at least written about?


texts: Would a black hole evaporate via Hawking radiation before you fall past the event horizon?

texts:
It takes an infinite amount of time for something to fall past the event horizon of a black hole from the perspective of someone outside the event horizon. Black holes also evaporate after a finite amount of time from an outsider's perspective  due to Hawking radiation.

Does this mean that you would never actually reach the event horizon if you fell into a black hole because the black hole would evaporate?


texts: Does such a heavenly body exist called a black dwarf? It would be a Brown dwarf that has cooled to the point it no longer gives off heat or light.


texts: So, my grandfather so graciously gave me his TASCO 49060700 60x700mm Spacestation Refractor Telescope, which is extremely wondrous. Any way, I found this answer to my 3x barlow lens, which I believe is saying multiply the magnification on the lens to the barlow. I've got three separate lenses; 25mm, 10mm, and a 4mm. My question is, do I multiply 25 by three(25 being the 25mm) and I get 75x magnification?


texts: Detect Passage of Massive Relativistic Object

texts:
I came across an interesting article that speculates that we could detect an object of significant mass ("space-ship size") moving through our galactic neighborhood at a substantial fraction of the speed of light with existing technology.

That got me wondering (for a sci-fi novel I'm writing) whether there would be evidence of such passage near the point in space where it occurred years or decades after such passage far from any star.

The CMB interactions mentioned in the article would spread from the point of passage at the speed of light so would have long departed the area. Is it likely that some artifact of passage would still be present, such as a change to the interstellar medium (change to ionization rates, fusion of lighter elements, etc)? How quickly would any such changes disperse? For purposes of the question, assume that scientific observations are possible at the point of suspected passage.


texts: If Planet Nine indeed exists, how large a impact event there should be to be seen from Earth?

texts:
Recently I've found this news article, A meteorite crashed into the Moon during total lunar eclipse in January, about a collision into the moon that happened while a lunar eclipse was under way. According to a paper{1}, it produced a flash that peaked about 4.2 magnitude, what puts it in the range visible to the naked eye, assuming a threshold around magnitude 5:

Despite visible from Earth, it was caused by a pretty small object, about 45kg, with impact energy about 1.5 ton TNT equivalent:

That made me wonder, if we were lucky enough, could we pinpoint Planet Nine position just by looking in its general direction and waiting for a large enough impact with a KBO, able to produce a visible flash?
Or instead of a visible flash, perhaps we could at least hope to detect the infrared glow from the heat produced. For example, assuming a Planet Nine about twice Earth radius at 800 AU, I estimate the amount of energy received from the sun in a Earth day to be about $10^{17}J$:
Python 3.8.5 (default, Sep  4 2020, 07:30:14)
[GCC 7.3.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> solar_constant_earth = 1362
>>> solar_constant_9th = solar_constant_earth * (1/800)**2
>>> solar_constant_9th
0.0021281250000000002
>>> 9th_cross_section = 3.1415 * (2 * 6350000)**2
  File "<stdin>", line 1
    9th_cross_section = 3.1415 * (2 * 6350000)**2
     ^
SyntaxError: invalid syntax
>>> cross_section_9th = 3.1415 * (2 * 6350000)**2
>>> daily_energy_input_9th = solar_constant_9th * cross_section_9th * 60 * 60 * 24
>>> daily_energy_input_9th
9.316555641045002e+16

This is about the estimated yield from the Tunguska event, so I think even a impactor as small as 100m across delivers the equivalent to a day worth of 9th total solar irradiation in a split second, so the infrared glow of the planet could be boosted a lot, briefly.
{1}. Madiedo, José M., et al. “Multiwavelength observations of a bright impact flash during the 2019 January total lunar eclipse”. Monthly Notices of the Royal Astronomical Society, vol. 486, no 3, julho de 2019, p. 3380–87. Silverchair, doi:10.1093/mnras/stz932. link


texts:
Recently, I have been going out to observe the ISS when it is within sight of my location.  I have noticed that the ISS, based on the time that I have to observe the space station during any given transit, moves at a fairly constant speed across the sky, depending on the degree of elevation and maybe some other factors related to the seeing conditions.

My question relates to the different course the space station takes when traversing over my location. There may be as long as several weeks when the ISS is not within viewing parameters for my location. Why does the course across the sky vary from time to time?


texts: Is the cluster of asteroids between Mars and Jupiter two dimensional as seen in every model of solar system shown in books or television? Or is it three dimensional as i think it should be?


texts: On the day of total solar eclipse why was early sunrise observed in India?

texts:
I am a middle school teacher from India(UTC+5:30). On August 21, 2017 morning at (17.385044, 78.486671) we observed an unusually early sunrise. It felt like its 7'O clock in the morning at 5:45 AM. And we had an unusually bright day. I'm sure it has to do something with the total solar eclipse but I don't exactly know what it is.

My students are persistently asking me the reason for this early sunrise but I don't have enough knowledge of astronomy to answer them. Can someone kindly answer why we observed this phenomenon?


texts: Why are the W UMa variable subtypes labelled "A" and "W"?

texts:
The W Ursae Majoris variables (eclipsing contact binary stars) are divided into the A- and W-types. As described in Wilson (1978) "On the A-type W UMa systems":

There are two recognized subcategories, called the A type
and W type by Binnendijk (1965, 1970). In the A types, the
more massive component is covered at primary eclipse and
the systems are found to be well overcontact (see, e.g., Mochnacki and Doughty 1972a, b; Lucy 1973; Wilson and Devinney
1973). That is, their surfaces substantially exceed the Roche
“inner contact surface.” W types have the lower-mass component covered at primary eclipse and are in thin or marginal
contact (see, e.g., Lucy 1973).

Is there any reason the letters "A" and "W" were chosen for these groups?
The above indicates two references by Binnendijk as the origin of the classification, unfortunately ADS provides no sources for the 1965 reference and the 1970 reference appears to be paywalled.

Binnendijk (1965) "The W Ursae Majoris Systems"
Binnendijk (1970) "The orbital elements of W Ursae Majoris systems"


texts: What does the Sun look like from Eris at its aphelion?

texts: At its aphelion (most distant location from the Sun) the outermost-known planet Eris is about 100 times as far from the Sun as Earth. What does the Sun look like from Eris' surface? Is there still a proper day or does the Sun look more like the brightest star in a night sky? Would it hurt to look into the Sun from Eris? And would it still be dangerous to look into the Sun with average binoculars?


texts:
Does the position of a star on a HR diagram depend on the magnitude system/color index used?

I made a CMD of a particular cluster using HST WFC3/UVIS data, and when I plotted $F275W vs F275W - F606W$, a particular star (at a given RA and dec) was present near the blue straggler region, but now when I plot $F438W vs F438W - F814W$, this same star (at the same RA,dec) was found near the start of the RGB.

Why is this happening?


texts: Which constellation would appear to revolve around Denab,Vega or Thuban when axis of the earth would point toward them?

texts: We have been calling the star by looking at which we can make out the direction of the North Pole the North Star. This was the only method at the disposal of the sailors during the days when they did not have any compass with them. When the axis of the earth would point toward Denab, Denab would become the North Star. When it would point toward Vega, Vega would become the North Star. Likewise, when the axis would point toward Thuban, Thuban would become the North Star. When we look at the Polaris from the earth, the Big Bear appears to be revolving around it. So I am curious to know which constellations would appear to be revolving around the Denab, Vega and Thuban when the axis of the earth would be pointing toward them due to wobbling of the earth.


texts: Maximum Amplitude of a Lissajous Orbiting Object in a L4 or L5 Position

texts:
I stumbled on The Lagrangian points during some wikipedia reading.  After looking at the gravity contours, I naturally come to the conclusion that the L4 & L5 should have a wave pattern and then found the Lissajous orbit page.  It states:

  Orbits about Lagrangian points L4 and L5 are dynamically stable in theory so long as the ratio of the masses of the two main objects is greater than about 25, meaning the natural dynamics keep the [third object] in the vicinity of the Lagrangian point even when slightly perturbed from equilibrium.

After reading it I started to wonder if there is a maximum possible amplitude (height of the peaks and troughs relative to the orbital plane of the second object) of the pattern?

Also, if there theoretically is none, for cases where it is extremely large, say larger than the 2 times the radius of the second orbiting object, what would the respective object weight ratios have to be to keep such a perturbed orbit stable for any realistic period of time?

FYI, I'm a computer scientist who loves reading about physical cosmology but can be kinda a noob sometimes. Please forgive me if I'm asking for the wrong parameters.

Edit: Here is an animation of 2010 TK7, Earth's first trojan asteroid, showing the wave pattern I'm referring to. Recall that my question is referring to the height of the peaks and troughs relative to Earth's orbital plane. Since the video is a top-down view, the peaks and troughs are going into and out of the screen.


texts: Are rising sea levels caused by the moon?

texts: If the moon is moving away at a distance of 1.48" per year (BBC), than wouldn't that mean the gravitational pull by the moon would weaken over time causing the tidal bulge to shrink?  Thus causing sea levels to rise?


texts: Telescope on drones to escape light pollution?

texts: Would it be possible to mount a telescope on a high quality drone and fly above the light pollution to get better star shots (if the wind allows it of course)?


texts: As the Sun moves along with the planets does the sun exhibit vertical movement? That is, does it traverse in different planes?


texts: Was the Earth-Sun distance ever calculated based on the time difference between night and day?

texts:
If we define sunrise and sunset as the time when the center of the Sun goes over the horizon then day time is a little bit shorter than night time because from a single point one cannot see a complete hemisphere. Computing backwards from a known Earth radius of around 6700km and a known Earth-Sun distance of around 150 million kilometers one can compute that the angle of the Sun shining on the Earth is 13,4/150.000 which comes to the day being roughly 5 seconds shorter than the night.

The radius of the Earth was already known to the ancient Greeks. You also need a clock that is accurate to at less than a second per day and a spot to observe the Sun rise and and Sun set at exact times. If you are not at the equator there will be differences in day time due to the tilted Earth axis but one could either measure directly at the equator or measure over a whole year and average it out.

Question: was this method ever used to estimate the distance between the Earth and the Sun?


texts: Can Earth be ejected out of the solar system this way?

texts:
I found this image of what maybe a model of our solar system. Without a credible source I'm not sure I am looking at a star or black hole that comes close to our solar system and how it could throw Earth out of orbit from the sun and/or solar system?

I found it while Googling for how a solar system travels through space and did a picture search with no luck.

Is this possible? And what am I looking at?


texts: We know that two celestial bodies rotate around a center of mass. How does this concept work in case of solar systems where there are several planets versus one/two stars? (Even if the center of mass lies within a star, the center of mass for every planet would be different.) How is it that the rotation of celestial bodies does not become unsteady?


texts:
Night sky objects always interested me, nowadays Im trying to observe and photograph some of these objects. My phone is iPhone 6S, i used SkyGuide app to find positions, NightCap to photograph. Im sure brightest star is Mirach according to SkyGuide app.

It's photographed at 00:30 at my local time (Istanbul, London + 3), SkyGuide says Mirach's azimuth was 77° 11’ 28” .


texts: Why are there no stars visible in cislunar space?

texts:
It’s very puzzling that the moon landing had no stars in the background, the ISS clips have no stars in the background. I listened to multiple astronaut interviews speak on what it looks like up in space and about half of them speak of the “darkest black space”. I’m sure there is a very good explanation for this.

Is star light only visible through the medium of earth atmosphere? But once in the vacuum of space where there is no medium they disappear? What’s the explanation?

Minute 47-49 stars, press conference all three Apollo 11 astronauts

BBC interview with Neil Armstrong only


texts: Before Voyager 2, what were the highest quality photos of Uranus and Neptune?

texts:
I'm in search of historical knowledge of the outer ice giants, which seems so hard to come by. Right now I would be happy with just a photo of each, the best photo we had of them before Voyager 2. Such a photo from the 60's to early 80's would be great. This will almost surely be from the Hale Telescope at the Palomar Observatory, because it's 5 meter primary mirror was the biggest for a long time.

Note: I'm not entirely sure that Neptune would even be a resolvable disk, but nevertheless I still want to see what our best photo of it (from that time) would be.

After googling this for so long, I've come to the conclusion that the best bet would be old astronomy books, which sadly, I do not have. Maybe someone here can help me out.


texts: How to calculate the thickness of the ice crust on a frozen ocean planet/moon?

texts:
How do I calculate the thickness of the upper ice layer on cold ocean worlds like Europa, Enceladus, Ganymede, ...? I'm asking this for a programm I'm currently writing.

Given/Known is: mass, radius, average density of metal (assume Fe) core, rock (assume MgSiO3) layer, ice (assume H2O) layer; internal heat from tidal heating, radioactive decay and residual formation heat; external heating from solar radiation (assume equal constant heating distributed over the entire surface or ignore it if it is irrelevant/minuscule); pressure of the atmosphere above (assume pure N2 with variable pressure or no atmosphere)

Wanted is: thickness frozen (crust) and molten layer

Bonus stuff: If easy adaptation of the formula for the calculation of the rocky layers crust thickness is possible I would appreciate it. Should it be possible, an adaptation to find the rocky crust thickness and the ice crust thickness on wolds where both are needed would be helpful.

Thanks for any answer and time spent of solving this.


texts: What type of planetary-mass object would Planet Nine be?

texts:
Given that Planet Nine is hypothesized to be 10-20 times the mass of the Earth orbiting the sun some 200-2500 AU out, what kind of planetary-mass object would it be?

Even given that it has apparently "influenced" several Trans-Neptunian objects, since its orbit is so large and so slow (approximately 25,000 years) it would take an awful long time to clear out its own orbit (especially given that we do not know how long it has been in that orbit), so it seems like it would not qualify as an actual planet under the rules that re-classified Pluto.

Since it orbits our sun, it wouldn't be an exoplanet nor a rogue planet.  And it sure seems too big to be called a dwarf planet.

A captured planet seems closest in other attributes, but it probably was not either a capture nor a re-capture, but more likely a partial ejection.

So what classification would it fall into?


texts: Will 1036 Ganymed's orbit be changed by its close encounter with Mars in 2176?

texts: In 2176, the asteroid Ganymed will come as close as 0.02868 AU (4,290,000 km / 2,670,000 mi) from Mars. That's pretty close to Mars imho. Can Mars' gravity alter Ganymed's orbit significantly in 2176 and if so, how much would it change? Just curious. Ganymed is a near-Earth object after all, and one at global killer size.


texts: In astronomy Is there a name for the exact time between solar noon and sunset?

texts:
Like there are names for various events such as sunset, sunrise, solar noon, solar midnight, astro, nautical and civil twilight, what exactly is name for time between sunset and solar noon. Afternoon it is but what exactly between these two points? Is golden hour the only subcategory for the afternoon?

I did come across the word midafternoon. similarly, midnight, midmorning and midevening. but then again midafternoon would mean 3 o clock or does it mean point between solar noon and sunset? because midnight in general is more acceptable as 12 o clock. is it?


texts: Do astronomers have an established, systematic way for saying what does or doesn't orbit what? (e.g. "Mars orbits Earth")

texts:
A recent comment

  An object far enough away can certainly orbit the Moon and the Earth (and the Sun) -- Mars, for instance does this. An object in the Earth-Moon L2 is also orbiting both the Earth and the Moon.

A recent comment about that comment:

  according to your way of thinking all solar system bodies orbit Mercury, except the Sun, which is just silly. Or does the Sun in fact orbit Mercury as well? I think your use of the word orbit is not workable, nor shared by almost anyone else.

So I'd like to ask if astronomers have an established, systematic way for saying what does or doesn't orbit what within the solar system, and if so, a link to point to in the future would be greatly appreciated!


texts: Do meteorites streak across the sky in the same direction?

texts:
Once while camping with my family as a child we all watched a meteor shower in the summer (in the month of August).

All the meteorites streaked across the sky in the same direction.

Obviously, this was the result of the Earth passing thru a group of meteors but I've always wondered.

Do meteorites always streak in the same direction? While I know it's not likely to be exactly the same direction, but generally speaking. Would one say meteorites always travel for example: east to west?

I thought this was a plausible fact since the Earth is travelling around the Sun in a constant direction, and additionally it's always rotating in the same direction.

While meteorites can travel in all directions. Does the Earth's gravity pull them straight down towards the surface resulting in the streak to be always in the same direction.


texts: How much light does Jupiter project onto the surface of Ganymede?

texts: I suppose the answer would be a range as the Jupiter-facing side of Ganymede passed from Jupiter's light side to its shadow side. I'd also like to know how much light the sun projects onto the surface of Ganymede as well. I'm also interested in day night cycle characteristics.


texts: absolute speed of bodies as observed by a distant observer

texts:
What does a distant observer see if two masses with a given velocity are close enough to each other that time is dilated ?

Scenario (using 2 point masses for simplicities sake):
Mass a: 1,00E+030 kg
Mass b: 2,00E+030

Kinetic energy:

mass a: 1,39037910021726E+046

mass b: 2,78075820043453E+046

this would mean a velocity of
Velocity: 149896229 m/s [ = c/2]
for both masses

distance between masses: 3960 m

using the formula for time dilation  the time would pass at a rate of ~0,5 at mass a and at a rate of ~0,8 at mass b

if both masses are flying parralel in the same direction does the observer see mass a flying with a speed of
74948115 m/s [= c/4] and mass b flying with a speed of 119916983 m/s [= c/2 *0.8]
?


texts: Could the movement of a PBH found in the outer solar system by microlensing be totally unpredictable and impossible to track after it was first detected?


texts: relation between azimuth angle of the sun and angle of the shodow

texts:
What is the relation between azimuth angle of the sun the bearing of an vertical object's shadow?

For example if the bearing of the shadow is 75° can we conclude that azimuth angle of the sun is 195°? Is the diagram below correct?


texts: What are some good telescopes for a programmer?

texts: I’ve never purchased a telescope and I was considering buying one. However, I wasn’t sure what to look for. I love to tinker and so a telescope that I can program with libraries such as SPICE would be great. Any ideas?


texts: What does gravity-wave noise resemble locally?

texts:
Now that we know that gravity waves exist,  we can consider to design a new unit of measurement,  i.e.  deciGravs (from dB) and we can predict what the backround noise of dG's is locally and in space.

Consider a theoretical high-res LIGO that can graph gravity waves here and far away,  we can ffwd the record to represent the dG's at human timeframes.

What are the loudest local waves? Can we see the moon as the loudest local wave,  followed by other planets and moons,  are local bodies much louder than local bh waves?

There is an expected 3D wave map type locally and in deep space that we can model with graphical animations? Can we draw it easily in 2D/3Dusing 5 lines of code for every body and lots of processing?

Perhaps it makes sense to define a frequency chart of dG's and astroHz and a bit like the electromagnetic waves,  and chart gravity-waves,  amplitude and frequency trends and types?

Perhaps supernovas and solar flares and many background waves appear on graviCharts.  Can we know what graviCharts and backround noise of gravity resembles here and far away?


texts:
I am very used to working with seeing in arcseconds, but sometimes I come across the seeing in cm, e.g. here.

I have looked online for a way to convert from one to the other, but I can't find any. How would this be done?


texts: How many stars can stay close to each other without collapsing?

texts:
Is it possible for two stars to exist close to each other?

"Close" is relative; let's assume that two stars are close to each other if they are at the center of the same solar system.

It's possible for this to happen with 3 stars. But what about more? How many stars can be the center of exactly one solar system without collapsing because of gravity?


texts: Could Hubble's Law simply be light's frequency decaying over time?

texts:
Is it proven that the frequency of EMR does not decay (at all, ever), and if not, could the observations that led to Hubble's Law simply be that the frequency of light decays over very large durations/distances?

If it does not decay innately simply due to duration, what about the various interactions it would have with particles / fields / "empty space" over very large distances; could these have a (reducing) effect on the frequency?


texts: Why are telescopes positioned in Lagrange points?

texts:
In this Wikipedia article about the list of space telescopes to be launched (which I assume is exhaustive), of the 11 telescopes yet to be launched, 6 will be positioned at the Sun-Earth L2 Lagrange point. Why is that so?

I read that it has something to do with lower fuel consumption, but I would like a more detailed answer.


texts: How loud was the asteroid that killed the dinosaurs?

texts:
Asteroid impacts on the Earth can be very loud when they break up in the atmosphere, like Chelyabinsk, captured in this video:

The Chelyabinsk asteroid break-up was estimated to be about 180dB at 3 miles, and was detected as far as 9000 miles away.
If asteroids don't break up, presumably they are extremely loud on impact as well.  How loud was the asteroid that killed the dinosaurs either on atmospheric entry or impact with the ocean?


texts: Where are we in an approximate timeline of the possibly habitable universe?

texts: Our universe is supposedly 13+ billion years old and our Sun is a third generation star. It seems to me that we are now in a relatively young stage of the universe. How many generations of stars will there be before the end of the universe? When is 'now', relative to the all possible timepoints in the universe, that life could appear?


texts: What would happen if an astronaut orbiting Earth was exposed to radiation?

texts: I know that astronauts are constantly being protected from radiation from the sun and the cosmos. They are normally very safe from the harmful effects of radiation but what if their protection wasn't effective at all? What would be the effects on the human body if it is exposed to radiation?


texts: Surface conditions of lonely (rogue) planets

texts:
The question How are rogue planets discovered? describes the difficulties in finding planets (or planet-sized objects) that are floating through space without being under the influence of any star or Galaxy system.

What would the possible surface conditions of these planets be? Could chemotrophic life arise on such planets?


texts: How do you calculate the effects of precession on elliptical orbits?

texts: Kepler's first law states that planets (and all celestial bodies orbiting another body) travel in elliptical orbits, which have well-known formulas that make it relatively easy to calculate the orbital elements and associated behavior. However, ongoing precession means that the orbit is constantly changing - and so the planet isn't actually traveling in the ellipse it originally set out on! You can calculate precession and its related effects (this question and answer are helpful), but is there any way to calculate how the elliptical orbit will be "deformed" by precession?


texts: What would the Earth's peri- and aphelion have to be in order to have the same seasons due to its orbit?

texts:
Imagine the Earth had no axial tilt but had seasons due to a very elliptical orbit. How elliptical would the Earth's orbit have to be in order to have about the same seasons as it has now (just with the difference that they'd be in both hemispheres the same)? Mercury has a very elliptical orbit. If we scaled Mercury's orbit to a semi-major axis at 1 au, would we have the very same seasons? Mercury's surface temperature in its summer is ~430 °C and in winter ~280 °C (values for daytime). I guess this would translate into a too high difference if the Earth's orbit was as elliptical as Mercury's; it would have to be a bit less elliptical for the same seasons as now.
How far would the Earth have to be from the Sun at its perihelion to have about 30 °C on the midlatitudes and at its aphelion to have about 0 °C?


texts: How strong does a light source on the Moon have to be to be visible from Earth?

texts: Flashes from some meteoroid impacts on the Moon can be seen with the naked eye. How much light must a future lunar base emit in order to be visible as a dot in the lunar night (like the flag of Tunisia)? I suppose it is a bit complicated and depends on the phase of the Moon, and that the new Moon is so close to the Sun.


texts: location of the sun on the celestial sphere

texts:
The Sun, in its apparent motion along the ecliptic through the year, passes over the background of distant stars. However, given that we can't observe those stars due to the brightness of the Sun, how were the ancient astronomers able to identify which star the Sun appears to be over or near to?

The only possible explanation I can come up with is that they observed the morning sky just before dawn (while stars were still visible) or the night sky just after sunset and so they couldn't really identify the precise location of the Sun on the celestial sphere but they could describe its position in rather general terms, which is why they might say, e.g. that the Sun is in the constellation of the Capricorn. Am I missing something?


texts: Can Fermi Bubbles be produced in non-spiral galaxies?

texts:
In 2010 observations with the Fermi Gamma-ray Space Telescope discovered giant bubbles which have been named Fermi Bubbles. Similar structures have also been discovered by Pshirkov et al. (2016) surrounding M31 (the Andromeda Galaxy).

Our galaxy and M31 are barred spirals. Could Fermi Bubbles also form around other galaxy types, for example lenticular or elliptical galaxies?


texts: How does one add false colour to a fits image

texts: I have an exposure of a star field with a small galaxy located near the centre. It is of course a greyscale image. I would like to add colours (realistic) to this image for aesthetic purposes. What software can I use to play around with colours that is Linux compatible and relatively easy to get the hang of? I've been using DS9 which has some colour options but to my knowledge doesn't quite produce a realistic colour image.